Polyarylene sulfide, typified by polyphenylene sulfide (which hereinafter may be referred to as PPS for short), is a resin having properties suitable for engineering plastics, such as excellent heat resistance, barrier properties, chemical resistance, electrical insulating properties, moist-heat resistance, and flame resistance. In addition, polyarylene sulfide can be molded by injection molding or extrusion molding into various molded parts, films, sheets, and fibers, and has been widely used in fields that require heat resistance and chemical resistance, such as various electrical and electronic parts, machine parts, and automotive parts.
As a specific process for producing this polyarylene sulfide, the process which involves reacting alkali metal sulfide such as sodium sulfide with a polyhalogenated aromatic compound such as p-dichlorobenzene in an organic amide solvent such as N-methyl-2-pyrrolidone has been proposed, which process has been widely utilized as an industrial process for producing polyarylene sulfide. However, this production process requires carrying out a reaction under the conditions of high temperature, high pressure, and strong alkaline, and further requires expensive high-boiling polar solvents such as N-methylpyrrolidone, thereby presenting a problem in that it is an energy-consuming process which costs much to recover solvents and requires high process cost.
On the other hand, as an alternative process for producing polyarylene sulfide, the process for producing polyarylene sulfide by heating cyclic polyarylene sulfide is disclosed. This process has been expected to provide polyarylene sulfide having a high molecular weight, a narrow molecular weight distribution, and a small weight loss when heated, but has had a problem in that, e.g., the reaction requires high temperature and a long time to complete the reaction of cyclic polyarylene sulfide (Patent Document 1 and Non-patent Document 1, for example).
The process in which, in converting cyclic polyarylene sulfide into polyarylene sulfide, various catalyst components (such as compounds effective to generate radicals and ionic compounds) are utilized to promote the conversion is known. Patent Document 2 and Non-patent Document 2 disclose as a compound effective to generate radicals a compound which generates sulfur radicals by, for example, being heated, specifically a compound containing a disulfide bond(s). Patent Documents 3 to 5 disclose a process using as an ionic compound an alkali metal salt of sulfur such as a sodium salt of thiophenol, for example, and as a Lewis acid a metal halide such as copper chloride (II), for example, as a catalyst. However, these processes also have a problem in that high temperature and a long time are required to complete the reaction of cyclic polyarylene sulfide, and there has been a need for a process for producing polyarylene sulfide at even lower temperature and in an even shorter time.